Re: [PATCH v2] USB: Add MSM USB Device Controller driver

[Brian Swetland <swetland@google.com>]

On Tue, Nov 9, 2010 at 6:54 PM, David Brownell <david-b@pacbell.net> wrote:
>
>
> --- On Tue, 11/9/10, Pavan Kondeti <pkondeti@codeaurora.org> wrote:
>
>> >> Hi Matthieu,
>> >>
>> >>> This look like the arc/chipidea/mips ehci otg
>> core.
>> >>
>> >> Yes. It is chipidea core for ARM.
>> >>> Why can't you reuse the ci13xxx_udc.c driver
>
> That basic approach is FAR PREFERABLE.  Fix
> the bugs once, tune once, and so forth, reuse
> the ULPI support, etc.  Work on more
> platforms, since the silicon IP is reused.
>
> You'll end up with more folk who can help
> maintain the driver too, since the pool of
> potential helpers won't be limited to those
> who have/use MSM hardware.
>
> Just be sure to cleanly factor the bus
> (PCI vs MSM-s ARM platform flavor and
> SoC glues (bus-related).  That factoring
> will likely be the hardest part; but there
> are examples of similar stuff in Linux today.

The main headache is that this particular IP has different bugs in
different instantiations (I know, for example, it exists in Tegra with
a different set of issues around fetching descriptor heads and cache
alignment, on MSM7201A after extensive testing we discovered there was
no reliable way of adding a descriptor to a list of transactions once
that queue was active, etc...), so things that work in one SoC may
break another, etc, etc, but that's part of the adventure I suppose.
I certainly agree that one unified driver is the way to go if you can
make it all work.

Brian